Combining particle size spectra from a mesocosm experiment measured using photographic and aperture impedance (Coulter and Elzone) techniques

Particle size spectra provide the fundamental descriptions of particle distributions. They are essential for relating particles to such oceanic properties as light scattering, particle sinking fluxes, and aggregation rates. Particle size spectra measured on a sample by two or more different techniques are rarely combined. Ideas from fractal theory have been used in this study to relate particle sizes obtained simultaneously in a mesocosm by two aperture impedance instruments (Coulter and Elzone particle counters) with those obtained by a photographic and image analysis system. Assuming all particles are consistent with each other only if all particles have a fractal dimension of about 2.3. The transformation of measured particle sizes to those of equivalent diameter of volume-conserving spheres decreased the apparent size of the particles in the photographic data set. As a result, the transformed data showed a smaller change in total particle volume than the raw data. The distribution of mass with respect to particle diameter is bimodal, with most of the mass centered in particles of about 0.5 mm apparent diameter. The availability of particle size spectra over such a large range has helped in their interpretation.